The current trend in connector design for those connectors utilized in the computer field is to provide both high density and high reliability connectors between various circuit devices. High reliability for such connections is essential due to potential system failure caused by improper connections of devices. Further, to assure effective repair, upgrade, testing and/or replacement of various components, such as connectors, cards, chips, boards, and modules, it is highly desirable that such connections be separable and reconnectable in the final product.
Pin-type connectors soldered into plated through holes or vias are among the most commonly used in the industry today. Pins on the connector body are inserted through plated holes or vias on a printed circuit board and soldered in place using a conventional mechanism. Another connector or a packaged semiconductor device is then inserted and retained by the connector body by mechanical interference or friction. The tin lead alloy solder and associated chemicals used throughout the process of soldering these connectors to the printed circuit board have come under increased scrutiny due to their environmental impact. The plastic housings of these connectors undergo a significant amount of thermal activity during the soldering process, which stresses the component and threatens reliability.
The soldered contacts on the connector body are typically the mechanical support for the device being interfaced by the connector and are subject to fatigue, stress deformation, solder bridging, and co-planarity errors, potentially causing premature failure or loss of continuity. In particular, as the mating connector or semiconductor device is inserted and removed from the connector attached to the printed circuit board, the elastic limit on the contacts soldered to the circuit board may be exceeded causing a loss of continuity. These connectors are typically not reliable for more than a few insertions and removals of devices. These devices also have a relatively long electrical length that can degrade system performance, especially for high frequency or low power components. The pitch or separation between adjacent device leads that can be produced using these connectors is also limited due to the risk of shorting.
Another electrical interconnection method is known as wire bonding, which involves the mechanical or thermal compression of a soft metal wire, such as gold, from one circuit to another. Such bonding, however, does not lend itself readily to high-density connections because of possible wire breakage and accompanying mechanical difficulties in wire handling.
An alternate electrical interconnection technique involves placement of solder balls or the like between respective circuit elements. The solder is reflowed to form the electrical interconnection. While this technique has proven successful in providing high-density interconnections for various structures, this technique does not allow facile separation and subsequent reconnection of the circuit members.
An elastomer having a plurality of conductive paths has also been used as an interconnection device. The conductive elements embedded in the elastomeric sheet provide an electrical connection between two opposing terminals brought into contact with the elastomeric sheet. The elastomeric material that supports the conductive elements compresses during usage to allow some movement of the conductive elements. Such elastomeric connectors require a relatively high force per contact to achieve adequate electrical connection, exacerbating non-planarity between mating surfaces. Location of the conductive elements is generally not controllable. Elastomeric connectors may also exhibit a relatively high electrical resistance through the interconnection between the associated circuit elements. The interconnection with the circuit elements can be sensitive to dust, debris, oxidation, temperature fluctuations, vibration, and other environmental elements that may adversely affect the connection.
In general, to provide a superior electrical performance path, the metal conductor should be short, and preferably wide to provide a low inductance environment. This becomes very difficult in some traditional contact structures using stamped metal since very small and wide contacts do not have much compliance as springs. As contacts get smaller and the spacing between them is reduced, the features on the contacts make them very intricate and difficult to manufacture.
Most electrical contacts are made by stamping and forming metal into precise shapes, then assembling them into a plastic insulator housing. These contact members are typically inserted into a plastic or insulating housing, which positions them and prevents them from touching an exposed metal portion against that of a neighboring contact. Design features are incorporated to provide retention within the housing, or maximize the flexural properties of the springs. These features must be incorporated into the traditional contact members themselves, often creating changes in the cross section of the electrical path, or extra metal in places that may add parasitic or stub effect that tend to degrade signal quality.
Traditional flexible circuit, on the other hand, use a thin layer of copper mated with a layer of polyimide or liquid crystal polymer. The very nature of the circuit is such that it can bend and flex without breaking the electrical circuit. These circuits are typically quite readily designed with close tolerance and specific geometries that typically do not degrade the electrical signal significantly. The conductive traces on flexible circuits, however, are too flexible for use in conventional connector assemblies. The conductive traces are too flexible to provide sufficient normal force to remain electrically connected to the circuit members. If a conductive trace on a flexible circuit was used in a traditional connector or socket, the contact would flex out of the way and not spring back as with normal contacts, resulting in an open circuit.